HI,
I'm new here.
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
Can you use a supermic to check BSPP threads? and do you need 55 degree wires?

HI,
I'm new here.
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
Can you use a supermic to check BSPP threads? and do you need 55 degree wires?

Hello gagegirl,

Welcome to The Cove Forums!

The "Three-Wire Method" is described in the Machinery's Handbook.
It provides you with the formula and a formula to calculate the most appropriate wire diameter.

Search in the Book for "Measuring Screw Threads."

Stijloor.

Hello gagegirl,

for the calculations you can use a Freeware
QMSys Threads PD - Software for Determining the Pitch Diameter of Threads
The program QMSys THREAD-PD enables the user to determine the pitch diameter of threads when the indicated values are specified as well as to determine the indicated values when the pitch diameter is specified. QMSys Threads PD is suitable for virtually all kinds of threads:
· external and internal
· symmetrical and asymmetrical
· single-start and multiple

Indicated values and pitch diameters are determined using measuring wires or balls by Berndt's iteration formulae from the publication EA - 10/10 "Guidelines on the Determination of Pitch Diameter of Parallel Thread Gauges by Mechanical Probing".

The correction for the measuring force is defined by Lechowski's methods. The optimum diameter of wires or balls is calculated by the formulae published in EA - 10/10.

HI,
I'm new here.
My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.
Can you use a supermic to check BSPP threads? and do you need 55 degree wires?

Welcome to the Cove.:bigwave:

What are BSPP threads?Are you referring to British Standard Pipe Threads(BSP in short)?
Supermic (short for Supermicrometer) is capable of giving you two readings in one go,id est,inch/mm,with an accuracy upto one millionth of an inch.

3-wire method is widely used for calibration of thread plug gages.

/Umang :D

Are these pipe threads straight or tapered? THe three wire method works well with a super micrometer for straight threads. For tapered threads, the method gets a little more difficult and would require a master tapered plug.

The most helpful people I have found for all things thread gage related in Thread Check Inc.

Two doucments that might help are:

http://www.threadcheck.com/html/catolog_page11.html

http://www.threadcheck.com/images/Three_Wire_Formulas.pdf

I notice that you are in Cleveland. I run a cal lab in Cleveland. If you need help with anything, please contact me. My goal is to be a resource for calibration in the Cleveland area. I am happy to help you get the equipment calibrated yourself. Of course, I would provide you with information on our services if you would like.

Yes, you can check BSPP threads on a supermic. It's helpful to have 55° wires, but 60° can do in a pinch- you just need to change your thread constant to reflect the change in wires.

I can provide you with that information- just PM me if you need it.

BSPP=British Standard Pipe Parallel

One of the first items to obtain would be the actual British Standard specifications for threaded ring and plug gages. The Brits use deferent requirements from what we have here in the USA. The specification will tell you the requirements and how to verify their conformity to the requirements.

A funny side note to this issue arose when a company I worked for decided that to save money (early 1980's) on the procurement of ring and plug gages by having their division in England buy the gages. The shinny new gages arrived from England with calibration certifications and they promptly started rejecting lot after lot of product. After much research it was found that gages manufactured to British Standards had much deferent thread form and tolerances than those manufactured to US Standards.

One of the first items to obtain would be the actual British Standard specifications for threaded ring and plug gages. The Brits use deferent requirements from what we have here in the USA. The specification will tell you the requirements and how to verify their conformity to the requirements.

British Standard Threads
BSPP = British Standard Pipe Parellel specified in ISO 228.
Neither BSPP nor BSP are authorized designations.
Avoid using BSP because confusion between BSPP and BSPT frequentally occurs. Clearification is mandatoary by standard number to assure the correct thread.
The threads series is nomenclated as: 'G' (example: G1/4)
BS 2779 has been retired and replaced in whole with ISO 228.
ISO 228/1 defines the product threads.
ISO 228/2 defines the gage parameters.

BSPT = British Standard Pipe Taper specified in ISO 7 and BS 21
BSPT is not an authorized designation.
The thread series is nomenclated as: 'R' but with and without additional lower case letters.
R = External Taper Thread
Rc = Internal Taper Thread
Rs = External Parellel Thread
Rp = Internal Parellel Thread
Beware, these parellel threads are not the same as the G-series threads. Always identify the applicable standard when dealing with British Standard Pipe Parellel threads.
The product threads defined in each standard are identical.
The gage systems defined in the two standards differs. BS 21 is less expensive to use because it requires fewer gage members.


A funny side note to this issue arose when a company I worked for decided that to save money (early 1980's) on the procurement of ring and plug gages by having their division in England buy the gages. The shinny new gages arrived from England with calibration certifications and they promptly started rejecting lot after lot of product. After much research it was found that gages manufactured to British Standards had much deferent thread form and tolerances than those manufactured to US Standards.There is no US gage maker that makes British Standard Pipe Gages to the appropiate standard. The US gage makers do not have the capability to accuratelly make the thread profile. Because of this they make a modified form to the thread form. They truncate the radisus from the gage and expect the end user to use alternate measurement methods to assure the thread form is accurate. Gages made in USA should be marked: 'Truncated' or: 'Modified'. Eather way is just a method of saying that the gaqes do not meet the requirements of the designated standard. Use caution when purchasing cutting tools for the same reason. Always specify 'Full Form' for gages and cutting tools to assure that the requirements of the standard are being met in your finished products.

Here in USA, way back to WW I, we have been modifying the British Standard Pipe thread form. The rest of the world uses the full form version of the thread, as specified by the standards. We now are making more for export. If your customer is not in USA, they are expecting the threads to be made to the standard, not to the USA bastardized version of the standard.

The R-series is designed to be a dry seal thread. The root and crest radii are intregal to make the dry seal connection.

Hi Wayne,

the Standard for BSPT threads is ISO 7/2.

Software QMSYS Threads and Gauges calculates:
- ISO Straight pipe thread acc. to ISO 228-1:2000; Gauges acc. to ISO 228-2:1987
- ISO Taper pipe thread R-Rp-Rc acc. to ISO 7-1:1994; Gauges acc. to ISO 7-2:2000 or BS 21:1985, System B

...the Standard for BSPT threads is ISO 7/2.

Actually, just like the ISO 228, the ISO 7 Has two parts:
ISO 7/1 for product thread.
ISO 7/2 for gages.

Software QMSYS Threads and Gauges calculates:
- ISO Straight pipe thread acc. to ISO 228-1:2000; Gauges acc. to ISO 228-2:1987
- ISO Taper pipe thread R-Rp-Rc acc. to ISO 7-1:1994; Gauges acc. to ISO 7-2:2000 or BS 21:1985, System BI am glad to see that the software is up to the current version of the standards because ISO 7/2 under went a major revision in 2000, changing the required gages and parting from BS 21 in gage design theory. Anyone measureing BSPT R-series threads should take care to have their gage system match their customer's gage system to avoid possible measurement irregularites on parts manufactured near the product limits.

Thanks, I would appreciate that. I'm working on calibrating G 1/2" and G 3/4" BSPP (British Standard Pipe Parallel). If there's any other information you need from me just let me know.

My company just notified me that they ordered "modified" American made threads for the G 1/2" and G 3/4"? What can I expect when those gages hit the manufacturing floor? Will the type of tap being used affect whether the thread gage will function properly?

My company just notified me that they ordered "modified" American made threads for the G 1/2" and G 3/4"? What can I expect when those gages hit the manufacturing floor? Will the type of tap being used affect whether the thread gage will function properly?The type of tap now make all the difference.
Modified tapped hole...
Full form gage will accuratelly reject.
Modified gage will accept, but the hole still does not meet the requirements of the standard.
Full form tapped hole...
Full form gage will accept.
Modified gage will accept.
I'm working on calibrating [modified American made] G 1/2" and G 3/4" BSPP (British Standard Pipe Parallel) [work plug gages]. If there's any other information you need from me just let me know.The pitch diameters should be stated on the handles of the gages. These pitch diameters will be the starting point for your calibration. I expect that the gage maker will have made the GO gage with a plus 0.0003" tolerance and the NOGO with a minus 0.0003" tolerance. I do not say this with certainity because the gages are modified by the gage maker from the standard, but these would be the UN-series tolerances for the similar size thread gages. I reccommend that you contact the gage maker to determine the actual values that were assigned, or check your original Detailed Inspection Report (Long Form Certificate) which will contain the manufacturing parameters.

Now are you ready for some serious math? I have attached two files.
First is the Thread Wire Best Sizes. You do not need this, just the your standard 14-TPI 60° thread wires.
Second is Thread Wire Constants. Use this page to calculate the appropiate constant for your 55° BSPP thread form.
I have not tested these formulas, so use with all due caution.

Finally, alert your Purchasing Department to avoid 'modified' or 'truncated' British Standard Pipe cutting tools and gages.

Hi Gagegirl,

I have attached a file with G 1/2", values in [mm] and [in]

British Standard Threads
BSPP = British Standard Pipe Parellel specified in ISO 228.
Neither BSPP nor BSP are authorized designations.
Avoid using BSP because confusion between BSPP and BSPT frequentally occurs. Clearification is mandatoary by standard number to assure the correct thread.
The threads series is nomenclated as: 'G' (example: G1/4)
BS 2779 has been retired and replaced in whole with ISO 228.
ISO 228/1 defines the product threads.
ISO 228/2 defines the gage parameters.

BSPT = British Standard Pipe Taper specified in ISO 7 and BS 21
BSPT is not an authorized designation.
The thread series is nomenclated as: 'R' but with and without additional lower case letters.
R = External Taper Thread
Rc = Internal Taper Thread
Rs = External Parellel Thread
Rp = Internal Parellel Thread
Beware, these parellel threads are not the same as the G-series threads. Always identify the applicable standard when dealing with British Standard Pipe Parellel threads.
The product threads defined in each standard are identical.
The gage systems defined in the two standards differs. BS 21 is less expensive to use because it requires fewer gage members.


There is no US gage maker that makes British Standard Pipe Gages to the appropiate standard. The US gage makers do not have the capability to accuratelly make the thread profile. Because of this they make a modified form to the thread form. They truncate the radisus from the gage and expect the end user to use alternate measurement methods to assure the thread form is accurate. Gages made in USA should be marked: 'Truncated' or: 'Modified'. Eather way is just a method of saying that the gaqes do not meet the requirements of the designated standard. Use caution when purchasing cutting tools for the same reason. Always specify 'Full Form' for gages and cutting tools to assure that the requirements of the standard are being met in your finished products.

Here in USA, way back to WW I, we have been modifying the British Standard Pipe thread form. The rest of the world uses the full form version of the thread, as specified by the standards. We now are making more for export. If your customer is not in USA, they are expecting the threads to be made to the standard, not to the USA bastardized version of the standard.

The R-series is designed to be a dry seal thread. The root and crest radii are intregal to make the dry seal connection.

Hi Wayne
I am new to this forum - first post
Perhaps this should be a new post, but it looks like you might have information I am looking for.
I need a charts listing tap drill min dept for BSPT and NPT
Also thread length.
The only chart I have been able to find is from Misumi and it is incomplete (only three sizes)
This chart is in misumiusa.com/uploadedFiles/Mold/m1435 catalog

I need a charts listing tap drill min dept for BSPT and NPT. Also thread length.Attached is a Tap Drill Size Chart which includes tap drill sizes for both the G-series and the NPT-series screw threads.

Lenght of taper screw threads is best controlled by a screw thread gage.

Does that answer your question?

Attached is a Tap Drill Size Chart which includes tap drill sizes for both the G-series and the NPT-series screw threads.

Lenght of taper screw threads is best controlled by a screw thread gage.

Does that answer your question?

Thanks for the imput
:thanks:
For your reference I found what I was looking for in 2 different catalogs
:evidence:
Fenn Tool Ltd
44 Springwood Drive
Springwood Industrial Estate
Braintree, Essex CM7 2YN
Tel: 01376 347566
Fax: 01376 550827 - Page 60 list thread length (Lm) for NPT & Rc

And the EMUGE Taper Pipe Tap Catalog
This one list minum tap drill dept - NPT page 126 & Rc page 131

I was looking for ...
To help others who are looking for the same information and that may find this thread, why not scan the pages and them post to this forum.

Attached you will find 1st catalog

11020

Attached is 2nd catalog Emuge catalog
11023

Here is a 3rd catalog from Presto which also has some of this info
11024

My questions are related to using the 3-wire method and a supermic for calibrating/checking thread plugs with.

No criticism of any info given in replies - just a personal observation.
I've noticed that many, when measuring thread pitch diameter (especially gauge calibration), use calcultions to "ensure" getting the last atoms of accuracy out of the final result. The slightlest deviation of the flank angle will probably give a greater deviation from the exact result than deviation pressure and the like.
My point is merely, "Don't shoot sparrows with an intercontinental missile" - or, if certainty and accuracy is an issue, measure more than "just" the pitch diameter ;)

Not quite on track with the original purpose of this thread but hpefully not irrelevant either :D

Wayne wrote:
“The thread series is nomenclated as: 'R' but with and without additional lower case letters.
R = External Taper Thread
Rc = Internal Taper Thread
Rs = External Parallel Thread
Rp = Internal Parallel Thread
Beware, these parallel threads are not the same as the G-series threads. Always identify the applicable standard when dealing with British Standard Pipe Parallel threads.
The product threads defined in each standard are identical”.

Is it me that’s not up-to-date? I’ve never seen Rs used and it isn’t in ISO 7-1. I’d consider R and Rs as being identical, but I've never seen it written as anything but R.

As most in here will know there are two types of Whitworth pipe threads (55O) – parallel and tapered, although (as Wayne emphasizes) the tapered R can be combined with both Rp and Rc, although the tolerance for Rp is not the same as for G type.

Just to clarify:
ISO 7-1 Pipe threads where pressure tight joints are made on the threads and
ISO 228-1 Pipe threads where pressure tight joints are not made on the threads

If it should be of interest to anyone then I made this (the enclosure) a few months ago for a customer. It should be useful for the larger tapered threads machined on CNC machines – less material for the thread profile tips to remove.